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Andrew Bell continues to question the exiting notion that energy
propagation in the cochlea involves an inertially-mediated fluid flow
coupled in to the basilar membrane as a traveling wave. He cites a recent
paper by Tianying Ren in Nature Neuroscience as evidence that the reverse
propagation of energy does not involve such a traveling wave. As observed
by David Mountain, the experimental design of Ren does not exclude a
reverse traveling wave. For measurement on the basilar membrane to
elucidate a reverse traveling wave requires that the reverse traveling wave
be larger in magnitude than any forward traveling wave at the same
frequency. This is most likely at a point basal to f2 - at a stimulus
frequency ratio that results in a 2f1-f2 DP generated from the nonlinear
interaction of f1 and f2 that is larger in the reverse than the forward

Comments by Martin Braun:
He did address the reverse traveling wave issue, and he found there is none.
He simultaneous measured stapes vibration and found that, for DPs, it
preceded that of BM vibration.
It is possible that Ren's phase-gradient data for stapes vibration involves
a wrapping error. Regardless of whether the reverse propagation of energy
involves a reverse traveling wave or a compressional wave, there is the
little issue of causality if the stapes vibration precedes the generation
of the source energy.

Robert Withnell